1. Field of the Invention
The present invention generally relates to a recording/reproducing apparatus and a recording/reproducing method.
2. Description of the Related Art
As the digitization of television signals and the like has recently started, there is a growing demand for an information recording medium to record a large amount of digital data. To that end, for example, in the optical disk field, reducing the size of the optical spot converged onto an optical disk is thought to be one of the basic solutions for achieving high-density recording. (Herein, an optical disk is described as a representative of disk-shaped media used in a recording/reproducing apparatus according to embodiments of the present invention. However, the disk-shaped media applicable to the present invention are not limited to the optical disks. Namely, the present invention may be applied to any disk-shaped medium including, but not limited to, a phase-change memory, a magneto-optical memory, and a holographic memory.) In order to achieve the high-density recording/reproducing by reducing the size of the optical spot, it is important to reduce a vibration amount of the disk surface, so-called “surface vibration”, when the disk is being rotated. To that end, there have been some proposed methods including a method of stabilizing the amount of the surface vibration by using stabilization means for aerodynamically stabilizing a disk medium having flexibility. The methods using such stabilization means for aerodynamically stabilizing a disk medium are described in, for example, Patent Documents 1 and 2.
Patent Document 1 describes a technique that, in a recording/reproducing apparatus, the distance between flat-plate stabilization means and a disk can be adjusted based on the rotational speed (rpm) of the disk and a tilt angle of the radius direction of the disk.
Patent Document 2 describes a technique that, in a recording/reproducing apparatus, by providing a spacer in rigid stabilization means, a certain interval (space) can be formed between the disk and the stabilization means.
As described in the above documents, by using a flexible medium as a recording disk and utilizing the aerodynamic functions of the stabilization means, stable recording/reproducing on the disk surface can be performed. Further, Patent Document 3 proposes stabilization means adapted to the magnetic disk field. Further, as modified stabilization means, Patent Document 4 describes curved stabilization means.
Further, as the demand for handling a large amount of digital data increases, there is also growing demand for faster data transmission rates. As a comprehensive example, the transmission rate 250 Mbps may be thought to be an important target. This is because this rate is required for recording broadcast HDTV footage. To be able to achieve this transmission rate across the entire disk surface, namely, in order to ensure such fast transmission rate at the inner part of the disk, fast driving to achieve 15,000 rpm becomes necessary. In addition, during the fast driving for recording/reproducing, it is also necessary to reduce the amount of the surface vibration from a viewpoint of the focus servo-following.    Patent Document 1: Japanese Patent Application Publication No: 2006-107699    Patent Document 2: Japanese Patent Application Publication No: 2006-344291    Patent Document 3: Japanese Patent Application Publication No: H1-502373    Patent Document 4: Japanese Patent Application Publication No: 2007-149311
However, in such a technique as described in Patent Document 1, the distance between the stabilization member (stabilization means) and the recording disk with respect to the rotational speed of the disk can be adjusted at specific distances stored in advance only. Therefore, it may not be possible to adaptively adjust the distance between the stabilization member and the recording disk to the optimal distance based on the considerations of the change over time and the load of the spindle motor.
On the other hand, in such a configuration as shown in Patent Document 2 where the flexible disk and the stabilization member on a rigid disk are synchronously rotated (with no relative speed) to stabilize air flow, the characteristics of disk-surface vibration may depend on the mechanical accuracy of the stabilization member itself. Therefore, it may be extremely difficult to obtain desirable characteristics in a very fast driving condition at, for example, 15,000 rpm or more and the rotational speed range where this technology can be used may be limited. Even if a glass substrate having excellent flatness is used, the disk surface vibration characteristics may be reduced to a range from about 20 μm to about 50 μm. In this case, for example, the maximum surface vibration acceleration at 10,000 rpm (maximum amplitude of frequency element less than 1.6 kHz) becomes in the order of several tens m/s2.
Further, the configuration as described in Patent Document 3 may be applied to a recording/reproducing method for disks that can be used only when the distance between the recording/reproducing head and the surface of the disk is relatively short. Therefore, it may be extremely difficult to apply this configuration (method) to a disk in which the recording/reproducing head is optically and macroscopically separated from the surface of the disk during operations. Even if the configuration of Patent Document 3 is modified so as to be applied to an optical disk, it may become necessary to form an opening through which two flexible disks are inserted to be installed in a position closer to the recording/reproducing head in the flat stabilization member for stabilizing the recording disks. Therefore, the opening may cause air disturbance which may limit the fast rotational speed of the disks and may not provide the desired characteristics when the fast-driven disk exceeds, for example, 10,000 rpm.